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<h1 class="topictitle1">Example: A switched disk cluster using independent disk pools</h1>
<div><p>A cluster using switched disk technology provides an alternative
to having the data replicated. In a switched disk cluster, the data is actually
contained in independent disk pools (also referred to as independent ASPs).</p>
<p>This example configuration provides the following:</p>
<ul><li>One switchable independent disk pool with an idle standby server. The
independent disk pool is contained within a collection of disk units that
are switchable.</li>
<li>Two-tier environment</li>
<li>Applications and data move together</li>
<li>Backup used for different work loads not associated with this application's
data</li>
<li>No data replication; only one copy of the data exists in this cluster</li>
</ul>
<br /><img src="rzaig502.gif" alt="A data CRG featuring a device domain and an external expansion unit" /><br /><p>Using this example, Node L and Node R belong to the same device domain.
Node L is currently operating as the primary node for two cluster resource
groups - an application CRG and a device CRG. Node R is the first (and only)
backup for both of the cluster resource groups. Data that is associated with
the device CRG is contained in a switchable resource such as an external expansion
unit (tower). Pertinent application information associated with the application
CRG is either stored in that same tower or is otherwise being replicated from
Node L to Node R. If Node L fails or needs to be taken down for administrative
reasons, then Node R becomes the primary node for both cluster resource groups.
Node R will take over the Internet Protocol (IP) address defined for the application
CRG. Node R will also assume ownership of the switchable resource defined
for the device CRG.</p>
<div class="note"><span class="notetitle">Note:</span> While Node L is down, system availability is exposed because there is
no backup should Node R also fail. When Node L recovers and rejoins the cluster,
it is made the backup for both cluster resource groups. If you want it to
again take on the role of primary, then an administrative switchover should
be performed.</div>
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaigscenarios.htm" title="Use these examples of typical cluster implementations to understand when, why, and how using clusters can be beneficial.">Examples: Cluster configurations</a></div>
</div>
<div class="relconcepts"><strong>Related concepts</strong><br />
<div><a href="../rzaly/rzalyscenarios.htm">Independent disk pools configurations</a></div>
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